System and method for permanent magnet motor control

ABSTRACT

A method of operating an electric motor is disclosed. The method includes: starting the electric motor in an open loop control mode; operating an estimator that estimates operating conditions of the electric motor; and, while the electric motor is in the open loop control mode, evaluating a first parameter of the estimator. The method further includes: in response to the evaluation of the first parameter, determining whether the estimator has converged; and in response to a determination that the estimator has not converged within a predetermined period of time after starting the electric motor, signaling a first fault condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/871,598, filed on Apr. 26, 2013, which claims the benefit of U.S. Provisional Application No. 61/638,937, filed on Apr. 26, 2012. This patent application is related to U.S. patent application Ser. No. 15/494,591, filed on the same day as this patent application. The entire disclosures of the applications referenced above are incorporated herein by reference.

FIELD

The present disclosure relates to sensorless motor control and to systems and methods for permanent magnet motor control.

BACKGROUND

The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Electric motors are used in a wide variety of industrial and residential applications including, but not limited to, heating, ventilating, and air conditioning (HVAC) systems. For example only, an electric motor may drive a compressor in an HVAC system. One or more additional electric motors may also be implemented in the HVAC system. For example only, the HVAC system may include another electric motor that drives a fan associated with a condenser. Another electric motor may be included in the HVAC system to drive a fan associated with an evaporator.

Power factor is an indicator of the relationship between current and voltage in a circuit. Power factor may be expressed as a value between negative one and positive one. A power factor correction (PFC) system generally operates to increase a circuit's power factor toward one, thereby increasing the circuit's use of real power and decreasing the amount of reactive power the circuit stores and returns to the source.

SUMMARY

In a feature, a method of operating an electric motor is disclosed. The method includes: starting the electric motor in an open loop control mode; operating an estimator that estimates operating conditions of the electric motor; and, while the electric motor is in the open loop control mode, evaluating a first parameter of the estimator. The method further includes: in response to the evaluation of the first parameter, determining whether the estimator has converged; and in response to a determination that the estimator has not converged within a predetermined period of time after starting the electric motor, signaling a first fault condition.

In further features, the electric motor is a compressor motor.

In still further features, the method further includes: switching to a closed loop control mode; while the electric motor is in the closed loop control mode, evaluating a second parameter of the estimator; and in response to the evaluation of the second parameter, selectively signaling a second fault condition.

In yet further features, the method further includes signaling both the first fault condition and the second fault condition using a common 1-bit signal.

In further features, the first parameter includes total flux linkage derivatives.

In yet further features, the evaluating the first parameter includes calculating a variance of the total flux linkage derivatives.

In still further features, the second parameter includes magnet flux linkages.

In further features, the evaluating the second parameter includes calculating a magnitude of the magnet flux linkages.

In yet further features, the evaluating the second parameter includes: comparing a measure of the second parameter with a threshold; incrementing a counter in response to the measure being greater than the threshold; and decrementing the counter in response to the measure being less than the threshold.

In still further features, the method further includes applying an upper limit to the counter, wherein the counter is incremented only up to the upper limit.

In further features, the method further includes signaling the second fault condition in response to the counter being decremented to a lower limit.

In yet further features, the method further includes, for a second predetermined period of time beginning at the switch to closed loop mode, suspending incrementing the counter and decrementing the counter.

In still further features, the evaluating the first parameter includes: comparing a measure of the first parameter to (i) a lower threshold and (ii) an upper threshold that is greater than the lower threshold; incrementing a counter in response to the measure being less than the lower threshold; and decrementing the counter in response to the measure being greater than the upper threshold.

In further features, the evaluating the first parameter further includes, in response to the measure being between the lower threshold and the upper threshold, decrementing the counter in response to the counter being decremented immediately previously.

In yet further features, the method further includes: determining that the estimator has converged in response to the counter being incremented to an upper limit.

In still further features, the evaluating the first parameter further includes applying a lower limit to the counter, wherein the counter is decremented only down to the lower limit.

In further features, switching to the closed loop control mode is performed in response to a determination that the estimator has converged.

In yet further features, switching to the closed loop control mode is performed at the predetermined time after starting the electric motor.

In a feature, a control system for an electric motor is disclosed. The control system includes: an estimator module that estimates operating conditions of the electric motor; and a rotor check module. The rotor check module: commands operation of the electric motor in an open loop control mode at startup of the electric motor; while the electric motor is in the open loop control mode, evaluates a first parameter of the estimator module; in response to the evaluation of the first parameter, determines whether the estimator module has converged; and in response to a determination that the estimator module has not converged within a predetermined period of time after starting the electric motor, signals a first fault condition.

In further features, the electric motor is a compressor motor.

In yet further features, the rotor check further: commands a transition to operating the electric motor in a closed loop control mode; while the electric motor is in the closed loop control mode, evaluates a second parameter of the estimator module; and in response to the evaluation of the second parameter, selectively signals a second fault condition.

In still further features, the rotor check module signals both the first fault condition and the second fault condition using a common 1-bit signal.

In further features, the first parameter includes total flux linkage derivatives.

In yet further features, the rotor check module evaluates the first parameter including calculating a variance of the total flux linkage derivatives.

In still further features, the second parameter includes magnet flux linkages.

In further features, the rotor check module evaluates the second parameter including calculating a magnitude of the magnet flux linkages.

In yet further features, the rotor check module evaluates the second parameter further including: comparing a measure of the second parameter with a threshold; incrementing a counter in response to the measure being greater than the threshold; and decrementing the counter in response to the measure being less than the threshold.

In still further features, the rotor check module further: applies an upper limit to the counter; and increments the counter only up to the upper limit.

In further features, the rotor check module signals the second fault condition in response to the counter being decremented to a lower limit.

In yet further features, the rotor check module, for a second predetermined period of time beginning when the transition to the closed loop control mode is commanded, suspends incrementing the counter and decrementing the counter.

In still further features, the rotor check module evaluates the first parameter including: comparing a measure of the first parameter to (i) a lower threshold and (ii) an upper threshold that is greater than the lower threshold; incrementing a counter in response to the measure being less than the lower threshold; and decrementing the counter in response to the measure being greater than the upper threshold.

In further features, the rotor check module evaluates the first parameter further including, in response to the measure being between the lower threshold and the upper threshold, decrementing the counter in response to the counter being decremented immediately previously.

In yet further features, the rotor check module determines that the estimator module has converged in response to the counter being incremented to an upper limit.

In still further features, the rotor check module evaluates the first parameter further including: applying a lower limit to the counter; and decrementing the counter only down to the lower limit.

In further features, the rotor check module commands the transition to the closed loop control mode in response to a determination that the estimator module has converged.

In yet further features, the rotor check module commands the transition to the closed loop control mode at the predetermined time after starting the electric motor.

In a feature, a system is disclosed. The system includes: a compressor including an electric motor; an inverter power module that includes a plurality of switches, that receives direct current (DC) power, and that powers the electric motor; an estimator module that estimates operating conditions of the electric motor; and a rotor check module. The rotor check module: commands operation of the electric motor in an open loop control mode at startup of the electric motor; while the electric motor is in the open loop control mode, evaluates a first parameter of the estimator module; in response to the evaluation of the first parameter, determines whether the estimator module has converged; in response to a determination that the estimator module has not converged a predetermined period of time after starting the electric motor, signals a first fault condition; commands a transition to operating the electric motor in a closed loop control mode; while the electric motor is in the closed loop control mode, evaluates a second parameter of the estimator module; and in response to the evaluation of the second parameter, selectively signals a second fault condition. The system further includes a pulse-width modulation (PWM) module that controls switching of the switches of the inverter power module based on at least one estimate of the estimator module.

In a feature, a system is disclosed. The system includes: a resistance determination module that determines a d-axis resistance of an electric motor and a Q-axis resistance of the electric motor as a function of a bulk current; an inductance determination module that determines a d-axis inductance of the electric motor and a Q-axis inductance of the electric motor as a function of the bulk current; a flux estimation module that generates an estimated flux of the electric motor based on the d-axis resistance of the electric motor, the Q-axis resistance of the electric motor, the d-axis inductance of the electric motor, and the Q-axis inductance of the electric motor; an angle estimation module that generates an estimated angle of the electric motor based on the estimated flux of the electric motor; and a pulse-width modulation (PWM) module that, based on the estimated angle of the electric motor, controls switching of an inverter that powers the electric motor.

In further features, the system further includes a bulk current determination module that determines the bulk current based on a Q-axis current of the electric motor and a d-axis current of the electric motor.

In yet further features, the system further includes a bulk current determination module that determines a second bulk current based on a Q-axis current of the electric motor and a d-axis current of the electric motor and that determines the bulk current based on the second bulk current and a maximum allowable value of the bulk current.

In still further features, the bulk current determination module sets the bulk current equal to the second bulk current divided by the maximum allowable value of the bulk current.

In further features, the system further includes a gain setting module that sets a gain, wherein at least one of: the resistance determination module determines the d-axis resistance further based on the gain; the resistance determination module determines the Q-axis resistance further based on the gain; the inductance determination module determines the d-axis inductance further based on the gain; the inductance determination module determines the Q-axis inductance further based on the gain; and the flux estimation module generates the estimated flux of the electric motor further based on the gain.

In yet further features, the gain setting module sets the gain based on at least one of the d-axis resistance, the Q-axis resistance, the d-axis inductance, and the Q-axis inductance.

In still further features, the gain setting module sets the gain based on a first average of the d-axis resistance and the Q-axis resistance and a second average of the d-axis inductance and the Q-axis inductance.

In further features, the gain setting module sets the gain based on a speed of the electric motor.

In yet further features, the system further includes a speed estimation module that generates an estimated speed of the electric motor based on the estimated angle of the electric motor, wherein the gain setting module sets the gain based on the estimated speed of the electric motor.

In still further features, the system further includes a bulk current determination module that determines the bulk current based on a Q-axis current of the electric motor and a d-axis current of the electric motor, wherein the gain setting module sets the gain based on the bulk current.

In yet further features: the flux estimation module that updates the estimated flux of the electric motor at a first rate; and the gain setting module updates the gain at a second rate that is equal to or slower than the first rate.

In a feature, a system is disclosed. The system includes: a compressor including an electric motor; an inverter power module that includes a plurality of switches, that receives direct current (DC) power, and that powers the electric motor; a resistance determination module that determines a d-axis resistance of an electric motor and a Q-axis resistance of the electric motor as a function of a bulk current; an inductance determination module that determines a d-axis inductance of the electric motor and a Q-axis inductance of the electric motor as a function of the bulk current; a flux estimation module that generates an estimated flux of the electric motor based on the d-axis resistance of the electric motor, the Q-axis resistance of the electric motor, the d-axis inductance of the electric motor, and the Q-axis inductance of the electric motor; an angle estimation module that generates an estimated angle of the electric motor based on the estimated flux of the electric motor; and a pulse-width modulation (PWM) module that controls switching of the switches of the inverter power module based on the estimated angle of the electric motor.

In a feature, a method is disclosed. The method includes: determining a d-axis resistance of an electric motor and a Q-axis resistance of the electric motor as a function of a bulk current; determining a d-axis inductance of the electric motor and a Q-axis inductance of the electric motor as a function of the bulk current; and generating an estimated flux of the electric motor based on the d-axis resistance of the electric motor, the Q-axis resistance of the electric motor, the d-axis inductance of the electric motor, and the Q-axis inductance of the electric motor. The method further includes: generating an estimated angle of the electric motor based on the estimated flux of the electric motor; and, based on the estimated angle of the electric motor, controlling switching of an inverter that powers the electric motor.

In further features, the method further includes determining the bulk current based on a Q-axis current of the electric motor and a d-axis current of the electric motor.

In yet further features, the method further includes: determining a second bulk current based on a Q-axis current of the electric motor and a d-axis current of the electric motor; and determining the bulk current based on the second bulk current and a maximum allowable value of the bulk current.

In still further features, the method further includes setting the bulk current equal to the second bulk current divided by the maximum allowable value of the bulk current.

In further features, the method further includes: setting a gain; and at least one of: determining the d-axis resistance further based on the gain; determining the Q-axis resistance further based on the gain; determining the d-axis inductance further based on the gain; determining the Q-axis inductance further based on the gain; and generating the estimated flux of the electric motor further based on the gain.

In yet further features, the method further includes setting the gain based on at least one of the d-axis resistance, the Q-axis resistance, the d-axis inductance, and the Q-axis inductance.

In still further features, the method further includes setting the gain based on a first average of the d-axis resistance and the Q-axis resistance and a second average of the d-axis inductance and the Q-axis inductance.

In further features, the method further includes setting the gain based on a speed of the electric motor.

In yet further features, the method further includes: generating an estimated speed of the electric motor based on the estimated angle of the electric motor; and setting the gain based on the estimated speed of the electric motor.

In still further features, the method further includes: determining the bulk current based on a Q-axis current of the electric motor and a d-axis current of the electric motor; and setting the gain based on the bulk current.

In further features, the method further includes: updating the estimated flux of the electric motor at a first rate; and updating the gain at a second rate that is equal to or slower than the first rate.

Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an example refrigeration system;

FIG. 2 is a functional block diagram of an example drive controller and an example compressor;

FIGS. 3A-3C are simplified schematics of example power factor correction (PFC) modules;

FIGS. 4A-4C are simplified schematics of example inverter power modules and exemplary motors;

FIG. 5 is a functional block diagram of a motor control module;

FIG. 6 is a functional block diagram of an example implementation of the estimator module of FIG. 5;

FIG. 7 is a functional block diagram of an example Luenberger observer;

FIG. 8 includes example graphs illustrating how d-axis resistance, Q-axis resistance, d-axis inductance, and Q-axis inductance may change with bulk current;

FIG. 9 is a flowchart depicting an example method of generating estimated position and estimated speed of a motor;

FIG. 10 is a flowchart depicting example operation of a method for determining estimator convergence in open loop and closed loop modes and for initiating transition from open loop to closed loop; and

FIG. 11 is a functional block diagram depicting an example implementation of the rotor check module of FIG. 5.

In the drawings, reference numbers may be reused to identify similar and/or identical elements.

DETAILED DESCRIPTION

Referring now to FIG. 1, a functional block diagram of a refrigeration system 100 is presented. The refrigeration system 100 may include a compressor 102, a condenser 104, an expansion valve 106, and an evaporator 108. According to the principles of the present disclosure, the refrigeration system 100 may include additional and/or alternative components. In addition, the present disclosure is applicable to other suitable types of refrigeration systems including, but not limited to, heating, ventilating, and air conditioning (HVAC), heat pump, refrigeration, and chiller systems.

The compressor 102 receives refrigerant in vapor form and compresses the refrigerant. The compressor 102 provides pressurized refrigerant in vapor form to the condenser 104. The compressor 102 includes an electric motor that drives a pump. For example only, the pump of the compressor 102 may include a scroll compressor and/or a reciprocating compressor.

All or a portion of the pressurized refrigerant is converted into liquid form within the condenser 104. The condenser 104 transfers heat away from the refrigerant, thereby cooling the refrigerant. When the refrigerant vapor is cooled to a temperature that is less than a saturation temperature, the refrigerant transforms into a liquid (or liquefied) refrigerant. The condenser 104 may include an electric fan that increases the rate of heat transfer away from the refrigerant.

The condenser 104 provides the refrigerant to the evaporator 108 via the expansion valve 106. The expansion valve 106 controls the flow rate at which the refrigerant is supplied to the evaporator 108. The expansion valve 106 may include a thermostatic expansion valve or may be controlled electronically by, for example, a system controller 130. A pressure drop caused by the expansion valve 106 may cause a portion of the liquefied refrigerant to transform back into the vapor form. In this manner, the evaporator 108 may receive a mixture of refrigerant vapor and liquefied refrigerant.

The refrigerant absorbs heat in the evaporator 108. Liquid refrigerant transitions into vapor form when warmed to a temperature that is greater than the saturation temperature of the refrigerant. The evaporator 108 may include an electric fan that increases the rate of heat transfer to the refrigerant.

A utility 120 provides power to the refrigeration system 100. For example only, the utility 120 may provide single-phase alternating current (AC) power at approximately 230 Volts (V) root mean squared (RMS) or at another suitable voltage. In various implementations, the utility 120 may provide three-phase power at approximately 400 Volts RMS or 480 Volts RMS at a line frequency of, for example, 50 or 60 Hz. The utility 120 may provide the AC power to the system controller 130 via an AC line. The AC power may also be provided to a drive controller 132 via the AC line.

The system controller 130 controls the refrigeration system 100. For example only, the system controller 130 may control the refrigeration system 100 based on user inputs and/or parameters measured by various sensors (not shown). The sensors may include pressure sensors, temperature sensors, current sensors, voltage sensors, etc. The sensors may also include feedback information from the drive controller 132, such as motor currents or torque, over a serial data bus or other suitable data buses.

A user interface 134 provides user inputs to the system controller 130. The user interface 134 may additionally or alternatively provide the user inputs to the drive controller 132. The user inputs may include, for example, a desired temperature, requests regarding operation of a fan (e.g., the evaporator fan), and/or other suitable inputs. The system controller 130 may control operation of the fan of the condenser 104, the fan of the evaporator 108, and/or the expansion valve 106.

The drive controller 132 may control the compressor 102 based on commands from the system controller 130. For example only, the system controller 130 may instruct the drive controller 132 to operate the compressor motor at a certain speed. In various implementations, the drive controller 132 may also control the condenser fan.

Referring now to FIG. 2, a functional block diagram of the drive controller 132 and the compressor 102 is presented. An electromagnetic interference (EMI) filter 202 reduces EMI that might otherwise be injected back onto the AC line by the drive controller 132. The EMI filter 202 may also filter EMI carried on the AC line.

A power factor correction (PFC) module 204 receives AC power from the AC line as filtered by the EMI filter 202. The PFC module 204 (described in more detail with reference to FIGS. 3A, 3B, and 3C) rectifies the AC power, thereby converting the AC input power into direct current (DC) power. The generated DC power is provided at positive and negative terminals of the PFC module 204. The PFC module 204 also selectively provides power factor correction between the input AC power and the generated DC power.

The PFC module 204 selectively boosts the AC power to a DC voltage that is greater than a peak voltage of the AC power. For example only, the PFC module 204 may operate in a passive mode, where the DC voltage generated is less than a peak voltage of the AC power. The PFC module 204 may also operate in an active mode, where the DC voltage generated is greater than the peak voltage of the AC power. A DC voltage that is greater than the peak voltage of the AC power may be referred to as a boosted DC voltage.

AC power having an RMS voltage of 230 V has a peak voltage of approximately 325 V (230 V multiplied by the square root of 2). For example only, when operating from AC power having an RMS voltage of 230 V, the PFC module 204 may generate boosted DC voltages between approximately 350 V and approximately 410 V. For example only, the lower limit of 350 V may be imposed to avoid unstable operating regimes of the PFC module 204. The limits may vary, such as with the actual AC input voltage value. In various implementations, the PFC module 204 may be able to achieve higher boosted DC voltages than 410 V. However, the upper limit of 410 V may be imposed to improve long-term reliability of components that would experience greater stress at higher voltages, such as components in a DC filter 206. In various implementations, the upper and/or lower limits may be varied dynamically.

The DC filter 206 filters the DC power generated by the PFC module 204. The DC filter 206 minimizes ripple voltage present in the DC power that results from the conversion of AC power to DC power. In various implementations, the DC filter 206 may include one or more series or parallel filter capacitors connected between the positive and negative terminals of the PFC module 204. In such implementations, the positive and negative terminals of the PFC module 204 may be connected directly to positive and negative terminals of an inverter power module 208.

The inverter power module 208 (described in more detail with reference to FIGS. 4A, 4B, and 4C) converts the DC power, as filtered by the DC filter 206, into AC power that is provided to the compressor motor. For example only, the inverter power module 208 may convert the DC power into three-phase AC power and provide the phases of the AC power to three respective windings of the motor of the compressor 102. In other implementations, the inverter power module 208 may convert the DC power into more or fewer phases of power.

A DC-DC power supply 220 may also receive the filtered DC power. The DC-DC power supply 220 converts the DC power into one or more DC voltages that are suitable for various components and functions. For example only, the DC-DC power supply 220 may reduce the voltage of the DC power to a first DC voltage that is suitable for powering digital logic and a second DC voltage that is suitable for controlling switches within the PFC module 204. For example only, the second DC voltage may be selectively applied to gate terminals of the switches. In various implementations, DC power may be provided by another DC power source (not shown)—for example, a DC power supply connected via a transformer to the main 230 VAC input.

In various implementations, the first DC voltage may be approximately 3.3 V and the second DC voltage may be approximately 15 V. In various implementations, the DC-DC power supply 220 may also generate a third DC voltage. For example only, the third DC voltage may be approximately 1.2 V. The third DC voltage may be derived from the first DC voltage using a voltage regulator. For example only, the third DC voltage may be used for core digital logic and the first DC voltage may be used for input/output circuitry of a PFC control module 250 and a motor control module 260.

The PFC control module 250 controls the PFC module 204, and the motor control module 260 controls the inverter power module 208. In various implementations, the PFC control module 250 controls switching of the switches within the PFC module 204, and the motor control module 260 controls switching of switches within the inverter power module 208. The PFC module 204 may be implemented with 1, 2, 3, or more phases.

A supervisor control module 270 may communicate with the system controller 130 via a communications module 272. The communications module 272 may include an input/output port and other suitable components to serve as an interface between the system controller 130 and the supervisor control module 270. The communications module 272 may implement wired and/or wireless protocols.

The supervisor control module 270 provides various commands to the PFC control module 250 and the motor control module 260. For example, the supervisor control module 270 may provide a commanded speed to the motor control module 260. The commanded speed corresponds to a desired rotational speed of the motor of the compressor 102.

In various implementations, the commanded compressor speed may be provided to the supervisor control module 270 by the system controller 130. In various implementations, the supervisor control module 270 may determine or adjust the commanded compressor speed based on inputs provided via the communications module 272 and/or parameters measured by various sensors (i.e., sensor inputs). The supervisor control module 270 may also adjust the commanded compressor speed based on feedback from the PFC control module 250 and/or the motor control module 260.

The supervisor control module 270 may also provide other commands to the PFC control module 250 and/or the motor control module 260. For example, based on the commanded speed, the supervisor control module 270 may command the PFC control module 250 to produce a commanded bus voltage. The supervisor control module 270 may adjust the commanded bus voltage based on additional inputs, such as operating parameters of the inverter power module 208 and the measured voltage of the incoming AC line.

The supervisor control module 270 may diagnose faults in various systems of the drive controller 132. For example only, the supervisor control module 270 may receive fault information from the PFC control module 250 and/or the motor control module 260. The supervisor control module 270 may also receive fault information via the communications module 272. The supervisor control module 270 may manage reporting and clearing of faults between the drive controller 132 and the system controller 130.

Responsive to the fault information, the supervisor control module 270 may instruct the PFC control module 250 and/or the motor control module 260 to enter a fault mode. For example only, in the fault mode, the PFC control module 250 may halt switching of the switches of the PFC module 204, while the motor control module 260 may halt switching of the switches of the inverter power module 208. In addition, the motor control module 260 may directly provide fault information to the PFC control module 250. In this way, the PFC control module 250 can respond to a fault identified by the motor control module 260 even if the supervisor control module 270 is not operating correctly and vice versa.

The PFC control module 250 may control switches in the PFC module 204 using pulse width modulation (PWM). More specifically, the PFC control module 250 may generate PWM signals that are applied to the switches of the PFC module 204. The duty cycle of the PWM signals is varied to produce desired currents in the switches of the PFC module 204. The desired currents are calculated based on an error between the measured DC bus voltage and a desired DC bus voltage. In other words, the desired currents are calculated in order to achieve the desired DC bus voltage. The desired currents may also be based on achieving desired power factor correction parameters, such as the shapes of current waveforms in the PFC module 204. The PWM signals generated by the PFC control module 250 may be referred to as PFC PWM signals.

The motor control module 260 may control switches in the inverter power module 208 using PWM in order to achieve the commanded compressor speed. The PWM signals generated by the motor control module 260 may be referred to as inverter PWM signals. The duty cycle of the inverter PWM signals controls the current through the windings of the motor (i.e., motor currents) of the compressor 102. The motor currents control motor torque, and the motor control module 260 may control the motor torque to achieve the commanded compressor speed.

In addition to sharing fault information, the PFC control module 250 and the motor control module 260 may also share data. For example only, the PFC control module 250 may receive data from the motor control module 260 such as load, motor currents, estimated motor torque, inverter temperature, duty cycle of the inverter PWM signals, and other suitable parameters. The PFC control module 250 may also receive data from the motor control module 260, such as the measured DC bus voltage. The motor control module 260 may receive data from the PFC control module 250 such as AC line voltage, current(s) through the PFC module 204, estimated AC power, PFC temperature, commanded bus voltage, and other suitable parameters.

In various implementations, some or all of the PFC control module 250, the motor control module 260, and the supervisor control module 270 may be implemented on an integrated circuit (IC) 280. For example only, the IC 280 may include a digital signal processor (DSP), a field programmable gate array (FPGA), a microprocessor, etc. In various implementations, additional components may be included in the IC 280. Additionally, various functions shown inside the IC 280 in FIG. 2 may be implemented external to the IC 280, such as in a second IC or in discrete circuitry. For example only, the supervisor control module 270 may be integrated with the motor control module 260.

FIG. 3A is a schematic of an example implementation of the PFC module 204. The PFC module 204 receives AC power via first and second AC input terminals 302 and 304. The AC power may be, for example, the AC power output by the EMI filter 202. In various implementations, the signals at the first and second AC input terminals 302 and 304 may both be time-varying with respect to an earth ground. The PFC module 204 outputs DC power to the DC filter 206 and the inverter power module 208 via a positive DC terminal 306 and a negative DC terminal 308.

An anode of a first rectifier diode 310 is connected to the second AC input terminal 304, and a cathode of the first rectifier diode 310 is connected to the positive DC terminal 306. An anode of a second rectifier diode 312 is connected to the negative DC terminal 308, and a cathode of the second rectifier diode 312 is connected to the second AC input terminal 304. Each of the rectifier diodes 310 and 312 may be implemented as one or more individual series or parallel diodes.

A switch block 320 is connected between the positive and negative DC terminals 306 and 308. The switch block 320 includes a first PFC leg 330 that includes first and second switches 332 and 334. The switches 332 and 334 each include a first terminal, a second terminal, and a control terminal. In various implementations, each of the switches 332 and 334 may be implemented as an insulated gate bipolar transistor (IGBT). In such implementations, the first, second, and control terminals may correspond to collector, emitter, and gate terminals, respectively.

The first terminal of the first switch 332 is connected to the positive DC terminal 306. The second terminal of the first switch 332 is connected to the first terminal of the second switch 334. The second terminal of the second switch 334 may be connected to the negative DC terminal 308. In various implementations, the second terminal of the second switch 334 may be connected to the negative DC terminal 308 via a shunt resistor 380 to enable measuring current flowing through the first PFC leg 330.

The control terminals of the switches 332 and 334 receive generally complementary PFC PWM signals from the PFC control module 250. In other words, the PFC PWM signal provided to the first switch 332 is opposite in polarity to the PFC PWM signal provided to the second switch 334. Short circuit current may flow when the turning on of one of the switches 332 and 334 overlaps with the turning off of the other of the switches 332 and 334. Therefore, both the switches 332 and 334 may be turned off during a deadtime before either one of the switches 332 and 334 is turned on. Therefore, generally complementary means that two signals are opposite for most of their periods. However, around transitions, both signals may be low or high for some overlap period.

The first PFC leg 330 may also include first and second diodes 336 and 338 connected anti-parallel to the switches 332 and 334, respectively. In other words, an anode of the first diode 336 is connected to the second terminal of the first switch 332, and a cathode of the first diode 336 is connected to the first terminal of the first switch 332. An anode of the second diode 338 is connected to the second terminal of the second switch 334, and a cathode of the second diode 338 is connected to the first terminal of the second switch 334.

The switch block 320 may include one or more additional PFC legs. In various implementations, the switch block 320 may include one additional PFC leg. As shown in FIG. 3A, the switch block 320 includes second and third PFC legs 350 and 360. The number of PFC legs included in the switch block 320 may be chosen based on performance and cost. For example only, the magnitude of ripple (voltage and current) in the DC output of the PFC module 204 may decrease as the number of PFC legs increases. In addition, the amount of ripple current in the AC line current may decrease as the number of PFC legs increase. However, parts costs and implementation complexity may increase as the number of PFC legs increases.

The second and third PFC legs 350 and 360 of the switch block 320 may be similar to the first PFC leg 330. For example only, the second and third PFC legs 350 and 360 may each include respective components for the switches 332 and 334, the diodes 336 and 338, and respective shunt resistors connected in the same manner as the first PFC leg 330.

The PFC PWM signals provided to the switches of the additional PFC legs may also be complementary. The PFC PWM signals provided to the additional PFC legs may be phase shifted from each other and from the PFC PWM signals provided to the first PFC leg 330. For example only, the phase shift of the PFC PWM signals may be determined by dividing 360 degrees (°) by the number of PFC legs. For example, when the switch block 320 includes three PFC legs, the PFC PWM signals may be phase shifted from each other by 120° (or 180° for two phases, or 90° for four phases, etc.). Phase shifting the PFC PWM signals may cancel ripple in the AC line current as well as the DC output.

The PFC module 204 includes a first inductor 370. The first inductor 370 is connected between the first AC input terminal 302 and the second terminal of the first switch 332. Additional inductors may connect the first AC input terminal 302 to additional PFC legs. For example only, FIG. 3A shows a second inductor 372 and a third inductor 374 connecting the first AC input terminal 302 to the second and third PFC legs 350 and 360, respectively.

A voltage may be measured across the shunt resistor 380 to determine current through the first PFC leg 330 according to Ohm's law. An amplifier (not shown), such as an operational amplifier, may amplify the voltage across the shunt resistor 380. The amplified voltage may be digitized, buffered, and/or filtered to determine the current through the first PFC leg 330. Current through other PFC legs may be determined using respective shunt resistors.

Additionally or alternatively, a resistor 382 may be connected in series with the negative DC terminal 308, as shown in FIG. 3B. Current through the resistor 382 may therefore indicate a total current output from the PFC module 204. Current through each of the PFC legs 330, 350, and 360 may be inferred from the total current based on the known phase timing of the current through the PFC legs 330, 350, and 360.

Any method of measuring or sensing current through any or all of the PFC legs 330, 350, 360 may be used. For example, in various implementations, the current through the first PFC leg 330 may be measured using a current sensor 387 (as shown in FIG. 3C). For example only, the current sensor 387 may be implemented in series with the first inductor 370. In various implementations, the current sensor 387 may include a Hall-effect sensor that measures the current through the first PFC leg 330 based on magnetic flux around the first inductor 370. Current through the PFC legs 350 and 360 may also be measured using associated current sensors 388 and 389, respectively.

The PFC module 204 may also include first and second bypass diodes 390 and 392. An anode of the first bypass diode 390 is connected to the first AC input terminal 302, and a cathode of the first bypass diode 390 is connected to the positive DC terminal 306. An anode of the second bypass diode 392 is connected to the negative DC terminal 308, and a cathode of the second bypass diode 392 is connected to the first AC input terminal 302.

The bypass diodes 390 and 392 may be power diodes, which may be designed to operate at low frequencies, such as, for example, frequencies less than approximately 100 Hz or approximately 200 Hz. Resistance of the bypass diodes 390 and 392 may be less than resistance of the inductors 370, 372, and 374. Therefore, when the switches 332 and 334 within the switch block 320 are not being switched, current may flow through the bypass diodes 390 and 392 instead of the diodes 336 and 338.

When the PFC module 204 is operating to create a boosted DC voltage, the boosted DC voltage will be greater than a peak voltage on the AC line. The bypass diodes 390 and 392 will therefore not be forward biased and will remain inactive. The bypass diodes 390 and 392 may provide lightning strike protection and power surge protection.

In various implementations, the bypass diodes 390 and 392 may be implemented with the rectifier diodes 310 and 312 in a single package. For example only, Vishay model number 26MT or 36MT or International Rectifier, model number 26 MB or 36 MB may be used as the bypass diodes 390 and 392 and the rectifier diodes 310 and 312. The rectifier diodes 310 and 312 carry current whether the PFC module 204 is generating a boosted DC voltage or not. Therefore, in various implementations, each of the rectifier diodes 310 and 312 may be implemented as two or more physical diodes connected in parallel. Current sensors may be used to measure PFC phase currents in series with the inductors 370, 372, and 374.

Referring now to FIG. 4A, a simplified schematic of a motor 400 and an example implementation of the inverter power module 208 is presented. The motor 400 is a component of the compressor 102 of FIG. 2. However, the principles of FIGS. 4A-4C may apply to other motors, including a motor of the condenser 104. The inverter power module 208 includes a switch block 402. In various implementations, the switch block 402 and the switch block 320 of the PFC module 204 may be implemented using a similar part. For example only, in FIG. 4A, a first inverter leg 410 includes first and second switches 420 and 422 and first and second diodes 424 and 426, which are arranged similarly to the switches 332 and 334 and the diodes 336 and 338 of FIG. 3A.

The switch block 402 receives the filtered DC voltage from the DC filter 206 via a positive DC terminal 404 and a negative DC terminal 406. The first terminal of the first switch 420 may be connected to the positive DC terminal 404, while the second terminal of the second switch 422 may be connected to the negative DC terminal 406. The control terminals of the switches 420 and 422 receive generally complementary inverter PWM signals from the motor control module 260.

The switch block 402 may include one or more additional inverter legs. In various implementations, the switch block 402 may include one inverter leg for each phase or winding of the motor 400. For example only, the switch block 402 may include second and third inverter legs 430 and 440, as shown in FIG. 4A. The inverter legs 410, 430, and 440 may provide current to windings 450, 452, and 454 of the motor 400, respectively. The windings 454, 452, and 450 may be referred to as windings a, b, and c, respectively. Voltage applied to the windings 454, 452, and 450 may be referred to as Va, Vb, and Vc, respectively. Current through the windings 454, 452, and 450 may be referred to as Ia, Ib, and Ic, respectively.

For example only, first ends of the windings 450, 452, and 454 may be connected to a common node. Second ends of the windings 450, 452, and 454 may be connected to the second terminal of the first switch 420 of the inverter legs 410, 430, and 440, respectively.

The inverter power module 208 may also include a shunt resistor 460 that is associated with the first inverter leg 410. The shunt resistor 460 may be connected between the second terminal of the second switch 422 and the negative DC terminal 406. In various implementations, respective shunt resistors may be located between each of the inverter legs 430 and 440 and the negative DC terminal 406. For example only, current through the first winding 450 of the motor 400 may be determined based on the voltage across the shunt resistor 460 of the first inverter leg 410. In various implementations, the shunt resistor of one of the inverter legs 410, 430, or 440 may be omitted. In such implementations, current may be inferred based on the measurements of the remaining shunt resistors.

Additionally or alternatively, a resistor 462 may be connected in series with the negative DC terminal 406, as shown in FIG. 4B. Current through the resistor 462 may therefore indicate a total current consumed by the inverter power module 208. Current through each of the inverter legs 410, 430, and 440 may be inferred from the total current based on the known phase timing of the current through the inverter legs 410, 430, and 440. Further discussion of determining currents in an inverter can be found in commonly assigned U.S. Pat. No. 7,193,388, issued Mar. 20, 2007, which is incorporated by reference herein in its entirety.

Any method of measuring or sensing current through any or all of the inverter legs 410, 430, and 440 may be used. For example, in various implementations, the current through the first inverter leg 410 may be measured using a current sensor 487 (shown in FIG. 4C). For example only, the current sensor 487 may be implemented between the first inverter leg 410 and the first winding 450. Current through the inverter legs 430 and 440 may also be measured using associated current sensors 488 and 489, respectively. In various implementations, current sensors may be associated with two of the inverter legs 410, 430, and 440. The current through the other one of the inverter legs 410, 430, and 440 may be determined based on an assumption that the current in the motor windings sums to zero.

Referring now to FIG. 5, an example implementation of the motor control module 260 of FIG. 2 is shown. The motor control module 260 controls switches within the inverter power module 208 to control voltages applied to the windings 454, 452, 450 (hereinafter, “windings_(a-c)”) of the motor 400. This may also be referred to as controlling the inverter power module 208 or as controlling the motor 400.

For example, when the motor 400 includes a three-phase motor, the motor control module 260 may apply voltages V_(a-c) to windings_(a-c), respectively. Voltages V_(a-c) may collectively be referred to as output voltages. Currents I_(a-c) are generated in the windings_(a-c), respectively, when voltages V_(a-c) are applied to the windings_(a-c). Currents I_(a-c) may collectively be referred to as winding currents. Currents in the windings_(a-c) produce magnetic flux about the windings_(a-c), and vice versa. The motor control module 260 generates the output voltages to control the winding currents and/or to control magnetic flux. The inverter power module 208 provides the switching voltage to the windings_(a-c).

The motor 400 includes a rotor (not shown) that rotates in response to the winding currents. The motor control module 260 controls the amplitude, duty cycle, and/or frequency of the output voltages to control the torque and speed of the rotor. The motor control module 260 may control the output voltages based on a commanded motor speed, which represents a desired rotational speed of the rotor. The motor control module 260 may control the output voltages further based on a commanded motor current, a commanded motor torque, and/or one or more other parameters.

The motor control module 260 may implement field oriented control of the motor 400. Accordingly, the motor control module 260 may map motor driving variables onto various frames of reference. Motor driving variables may include requested current/voltage values used to control the motor 400 as well as measured currents/voltages. For example, motor driving variables may include measured currents I_(a-c) through the windings_(a-c) and voltage requests used by the motor control module 260 to apply voltages V_(a-c) to the windings_(a-c).

The motor control module 260 may map motor driving variables in an abc frame of reference (FoR), an αβ FoR, a qdr FoR, a qdv FoR, and/or one or more other FoRs. The qdv FoR is the FoR for the commanded speed. The abc FoR may represent, for example, a three-phase stator frame based on the windings_(a-c). Each of the measured currents I_(a-c) may be mapped onto respective axes a, b, and c of the abc FoR. Additionally, the motor control module 260 may map requested voltages corresponding to voltages V_(a-c) in the abc FoR.

The αβ FoR includes stationary, stator-based x and y coordinates onto which the motor driving variables are projected. The qdr FoR is a rotating FoR that corresponds to the rotor and rotates in sync with the rotor. Accordingly, the qdr FoR is based on an angle of the rotor.

The motor control module 260 may transform motor driving variables from one FoR to another FoR. For example, the motor control module 260 may transform currents represented in the abc FoR into currents represented in the αβ FoR and vice versa. The motor control module 260 may transform motor driving variables from the abc FoR to the αβ FoR using a numerical transformation. The motor control module 260 may transform motor driving variables from the αβ FoR to the qdr FoR based on the angle of the rotor. Additionally or alternatively, the motor control module 260 may transform motor driving variables into an arbitrary FoR rotating at a specific speed, and this speed could be chosen as the commanded speed.

The motor control module 260 controls the inverter power module 208 based on the commanded speed from the supervisor control module 270 of FIG. 2. In various implementations, a filter module 501 may filter the commanded speed from the supervisor control module 270 of FIG. 2. In these implementations, the output of the filter module 501 is referred to below as the commanded speed ω_(v).

In open loop mode, the actual speed of the rotor will generally follow the commanded speed ω_(v), assuming that the commanded speed ω_(v) does not change too quickly. As a result, the coefficients of the low-pass filter and/or rate limiter of the filter module 501 may be chosen so that the rotor acceleration can keep up with changes in the commanded speed ω_(v) output from the filter module 501. Otherwise, rotor synchronization may be lost. In various implementations, the filter module 501 may implement a ramp function, which updates the commanded speed ω_(v) by up to a maximum increment during each predetermined interval of time.

The motor control module 260 may control the motor 400 based on a commanded FoR (e.g., a qdv FoR) when operating in open loop mode. The qdv FoR is associated with the commanded speed ω_(v) of the rotor and a commanded angle (θ_(v)) of the rotor. A commanded angle generation module 502 may determine the commanded angle θ_(v), such as by integrating the commanded speed ω_(v).

The motor control module 260 may operate in various modes, such as open loop mode or closed loop mode. For example only, the motor control module 260 may operate in open loop mode when starting the motor 400 and later transition to operating in closed loop mode. When operating in open loop mode, the rotor will tend to synchronize with the commanded speed ω_(v), especially when the motor control module 260 is operating the rotor at slower speeds. However, the actual rotor angle may differ from the commanded angle θ_(v) because of a load applied to the motor 400. For example, a change in load while operating in open loop mode may change a phase difference between the commanded angle θ_(v) and the actual rotor angle.

A rotor check module 503 monitors estimator parameters from an estimator module 504. The estimator module 504 may also be referred to as an estimator. The rotor check module 503 determines whether and when estimation has converged—i.e., whether and when the estimator module 504 is correctly tracking the actual operation of the motor 400. If the estimator does not converge, or if the estimator converges but then diverges, the rotor check module 503 may signal a rotor fault. In response to the rotor fault, the motor 400 may be shut down or another operating mode may be entered to attempt to bring the estimator back in line with motor operation.

In response to the one or more estimates of the estimator module 504 (e.g., flux estimates and/or a metric of the flux estimates) suitably converging after startup of the motor 400, the rotor check module 503 may generate a transition signal. In response to the transition signal, an angle/speed determination module 508 may transition from using open loop speed and angle values to closed loop speed and angle values. Further information regarding example implementations of the transition from open loop to closed loop and estimator convergence can be found in commonly assigned patent application Ser. No. 12/852,625, filed Aug. 9, 2010, now U.S. Pat. No. 8,344,706, issued Jan. 1, 2013, and in commonly assigned patent application Ser. No. 12/570,504, filed Sep. 30, 2009, now published as U.S. Pub. No. 2011/0068724, the disclosures of which are hereby incorporated by reference in their entirety.

The estimator module 504 estimates the speed (ω_(est)) and angle (θ_(est)) of the rotor. The estimator module 504 may determine the estimated speed ω_(est) based on the estimated angle θ_(est). For example, the estimator module 504 may differentiate and filter the estimated angle θ_(est) over a period of time to determine the estimated speed ω_(est).

The estimator module 504 may determine the estimated angle θ_(est) based on various motor driving variables. For example, the motor driving variables may include V_(a-c) to be applied to the windings_(a-c), I_(a-c) measured in the windings_(a-c), alpha-beta variables, and qdv variables. Additionally, the estimator module 504 may determine the estimated angle θ_(est) based on the commanded speed ω_(v). The estimator module 504 may include a state observer (e.g., a Luenberger observer) to determine the estimated angle θ_(est) and the estimated speed ω_(est) based on the motor driving variables. Further description of sensorless control systems and methods can be found in U.S. Pat. No. 6,756,757, issued Jun. 29, 2004, U.S. Pat. No. 7,208,895, issued Apr. 24, 2007, U.S. Pat. No. 7,342,379, issued Mar. 11, 2008, and U.S. Pat. No. 7,375,485, issued May 20, 2008, which are incorporated herein by reference in their entirety.

A current determination module 506 may measure the currents I_(a-c) of the windings_(a-c) (hereinafter “measured currents”). In various implementations, two of the currents I_(a-c) may be measured and the other one of the currents I_(a-c) may be determined knowing that the sum of the (three) currents I_(a-c) equals zero. The estimator module 504 may use the measured currents to generate the estimated angle θ_(est) and the estimated speed ω_(est). Stated broadly, the estimator module 504 estimates a total motor flux and a magnet flux, and the estimator module 504 generates the estimated angle and the estimated speed based on at least one of the estimated magnet flux and the estimated total flux. The estimator module 504 estimates the total motor flux and the magnet flux as a function of the motor driving variables. The motor driving variables include, among other things, motor resistances and motor inductances. The estimator module 504 determines bulk current based on the measured currents and determines the motor resistances and motor inductances as a function of the bulk current.

The angle/speed determination module 508 generates an output angle θ_(r) and an output speed ω_(r) based on the currently enabled mode, such as open loop mode or closed loop mode. The angle/speed determination module 508 may set the output angle θ_(r) equal to the commanded angle θ_(v) when operating in open loop mode and may set the output angle θ_(r) equal to the estimated angle θ_(est) when operating in closed loop mode.

When the rotor check module 503 instructs a transition from open loop mode to closed loop mode, the angle/speed determination module 508 gradually adjusts the output angle θ_(r) from the commanded angle θ_(v) to the estimated angle θ_(est). This gradual adjustment may minimize transient current demands when transitioning from open loop mode to closed loop mode, which may prevent disruption of current control (described below) and/or estimation of the estimated angle θ_(est). The gradual adjustment may therefore improve stability during transitions and allow for starting the motor 400 more reliably, especially under higher loads.

The angle/speed determination module 508 may set the output speed ω_(r) equal to the commanded speed w, when operating in open loop mode. The angle/speed determination module 508 may set the output speed ω_(r) equal to the estimated speed ω_(est) when operating in closed loop mode. In various implementations, the angle/speed determination module 508 may immediately switch the output speed ω_(r) from the commanded speed ω_(v) to the estimated speed ω_(est) when the rotor check module 503 instructs a transition from open loop mode to closed loop mode. The angle/speed determination module 508 may also set the output (rotor) speed ω_(r) as a function of the estimated speed ω_(est) and the commanded speed ω_(v).

The rotor check module 503 may also instruct a change from closed loop mode back to open loop mode. For example only, a transition back to open loop mode may be performed when error conditions are observed, such as a lost rotor or other abnormal operating conditions. The angle/speed determination module 508 may therefore also switch the output speed ω_(r) from the estimated speed ω_(est) back to the commanded speed ω_(v), and switch the output angle θ_(r) from the estimated angle θ_(est) back to the commanded angle θ_(v). In various implementations, similarly to the transition from open loop mode to closed loop mode, switching the output speed ω_(r) may be performed immediately, while switching the output angle θ_(r) may be performed gradually.

In various implementations, additional modes may be supported. For example only, three, four, or more modes may be supported. The rotor check module 503 may instruct the angle/speed determination module 508 to transition from one of the modes to another. During each transition, the angle/speed determination module 508 may switch the output speed ω_(r) immediately to a speed corresponding to the selected mode. Alternatively, the output speed ω_(r) may be ramped toward the speed of the selected mode. Further, the angle/speed determination module 508 ramps the output angle θ_(r) toward an angle corresponding to the selected mode. The rotor check module 503 may instruct the angle/speed determination module 508 to transition from one of the modes to another using a transition signal. For example, the transition signal may specify a target mode to which the angle/speed determination module 508 should transition.

A speed loop control module 510 generates a demanded torque signal calculated to match the output speed ω_(r) to the commanded speed ω_(v). In various implementations, the speed loop control module 510 may be bypassed in open loop mode. In closed loop mode, the output speed ω_(r) is equal to the estimated speed ω_(est) of the motor 400. Therefore, the speed loop control module 510 may generate the demanded torque signal in order to keep the speed of the motor 400 approximately equal to the commanded speed ω_(v). For example only, when the output speed ω_(r) is less than the commanded speed ω_(v), the speed loop control module 510 may increase the demanded torque, and vice versa.

An Idr injection module 512 generates a d-axis current (Idr) demand based on the DC bus voltage, the demanded torque signal, and the commanded speed ω_(v). The Idr demand is used by current control, described below, for Idr injection, which may also be referred to as field weakening or phase advance. In various implementations, the Idr injection module 512 may adjust the Idr demand based on an out of volts (OOV) signal, described below, and measured current.

A torque mapping module 514 generates a Q-axis current (Iqr) demand based on the demanded torque signal. Torque may also be generated by the Idr demand and therefore, the torque mapping module 514 may determine the Iqr demand based also on the Idr demand or the actual Idr. For example only, the torque mapping module 514 may implement a maximum current limit. In various implementations, the torque mapping module 514 may compare a combination of the Idr demand and the Iqr demand to the maximum current limit, and reduce one or both of the demands when the combination exceeds the maximum current limit. In various implementations, the torque mapping module 514 may limit only the Iqr demand. For example only, the maximum current limit may be a root mean square limit, such as 25 Amps_(rms).

When the torque mapping module 514 is limiting the Iqr demand to meet the maximum current limit, the torque mapping module 514 may output a limit signal to the speed loop control module 510. When the limit signal is received, the speed loop control module 510 may temporarily suspend increasing the demanded torque. In addition, the speed loop control module 510 may also temporarily suspend increasing the demanded torque based on the OOV signal.

For example only, the speed loop control module 510 may attempt to match the output speed ω_(r) to a reduced version of the commanded speed ω_(v). Alternatively or additionally, the speed loop control module 510 may selectively suspend error summing and/or integrating operation that would lead to increasing the demanded torque. In other words, when the torque mapping module 514 indicates, via the limit signal, that the maximum current limit is reached, the speed loop control module 510 may stop increasing the demanded torque because the present demanded torque already cannot be achieved within the maximum current limit.

A current control module 516 determines voltage commands Vqr and Vdr, in the qdr FoR, based on the current demands Iqr and Idr. The voltage commands Vqr and Vdr may be a Q-axis voltage command and a d-axis voltage command, respectively. In various implementations, the current control module 516 may determine the voltage commands Vqr and Vdr based also on the measured currents. In various implementations, the current control module 516 may attempt to match the measured currents to the Iqr and Idr demands by adjusting the voltage commands Vqr and Vdr. In various implementations, the current control module 516 may also receive the output speed ω_(r).

An abc to qdr module 520 maps the measured currents I_(a-c) onto the qdr FoR based on the output angle θ_(r). The resulting mapped current may be referred to as Iqdr, and may include Iqr and Idr components. The measured currents used by components of the motor control module 260, such as the current control module 516 and the estimator module 504, may therefore use the Iqdr representation of the measured currents.

A qdr to αβ module 522 may transform the voltage commands Vqr and Vdr from the qdr FoR to the αβ FoR, thereby generating a voltage request in the αβ FoR (hereinafter “voltage request”). The voltage request may indicate the voltages to be applied to the windings_(a-c). The qdr to αβ module 522 may perform the transformation based on the output angle θ_(r), and in various implementations, may perform the transformation based on the output speed ω_(r).

A pulse-width modulation (PWM) module 524 generates duty cycle signals to control the inverter power module 208 using PWM. For example only, the PWM switching frequency may be approximately 5 kHz or approximately 10 kHz. In various implementations, the inverter power module 208 and the motor 400 have three phases, and the PWM module 524 generates three duty cycle signals, one for each inverter leg.

In various implementations, each leg of the inverter power module 208 includes a pair of complementary switches, and each of the duty cycle signals is therefore converted into complementary duty cycle signals, one for each of the complementary switches. For example only, referring to FIG. 4A, the switch 420 and the switch 422 of the first inverter leg 410 may be controlled with complementary duty cycles.

In various implementations, to prevent a short circuit condition, where both the switches 420 and 422 are on simultaneously, the complementary duty cycles may be adjusted so that a switch is not turning on at the same time the other switch is turning off. In other words, the off-times of the two switches are partially overlapped.

The PWM module 524 determines the duty cycle signals based on the DC bus voltage and the voltage requests from the qdr to αβ module 522. For example only, the PWM module 524 may transform the voltage request from the αβ FoR to the abc FoR to determine three voltage demands, hereinafter Vr_(a), Vr_(b), and Vr_(c) (collectively Vr_(a-c)), corresponding to the windings_(a-c), respectively.

When the voltage demands cannot be met given the present DC bus voltage, the drive controller 132 is defined to be operating in the OOV state. For example only, a maximum duty cycle may be defined in the PWM module 524. If the voltage demands would result in one of the duty cycles being greater than the maximum duty cycle, the drive controller 132 is operating in the OOV state.

In various implementations, the maximum duty cycle may be set to be less than 100%, such as 96%, 95%, or 92%. The maximum duty cycle limit may be set based on requirements for accurate measurement of the winding currents I_(a-c). A corresponding minimum duty cycle limit may also be defined. For example only, the minimum duty cycle limit may be equal to one minus the maximum duty cycle limit (e.g., 1−0.96=4%, 1−0.95=5%, etc.).

In various implementations, the motor 400 may respond not to the winding voltages themselves, but instead to differences between the winding voltages. As a simplistic example, applying 50 Volts to a first winding and 150 Volts to a second winding may be equivalent to applying 0 Volts to the first winding and 100 Volts to the second winding. Therefore, even if one of the voltage demands may exceed an available voltage, the PWM module 524 may shift the voltage demands when generating the duty cycles.

In such implementations, the PWM module 524 may determine that the drive controller 132 is in the OOV state when a difference between any two of the three voltage demands is greater than the available voltage. For example only, the available voltage may be equal to the DC bus multiplied by the maximum duty cycle. In various implementations, the PWM module 524 may shift the duty cycles such that one of the duty cycles is set to zero. Alternatively, the PWM module 524 may shift the duty cycles such that the duty cycles are centered about a middle duty cycle, such as 50%. In various implementations, the PWM module 524 may shift the duty cycles using one or the other of these approaches, depending on an operating mode. For example only, the PWM module 524 may shift the duty cycles such that the lowest duty cycle is set to zero when the motor 400 is operating at speeds above a predetermined threshold.

In the OOV state, the difference between the duty cycles corresponding to the voltage demands is greater than the difference between the minimum and maximum duty cycles. Therefore, when operating in the OOV state, the PWM module 524 may scale the voltage demands down before generating the duty cycles. Equivalently, the PWM module 524 may scale the duty cycles. In various implementations, the PWM module 524 may scale the duty cycles or voltage demands as little as possible, such that one of the duty cycles is set to the minimum duty cycle, and one of the duty cycles is set to the maximum duty cycle.

The scaling factor is an indication of how far OOV the drive controller 132 currently is. The scaling factor may be referred to as OOV magnitude, and may be included in the OOV signal. In the OOV state, the PWM module 524 sets an OOV flag to a first value, such as 1. When not in the OOV state, the PWM module 524 sets the OOV flag to a second value, such as 0. The OOV flag may be included in the OOV signal.

A quantity called OOV amount may be determined based on the OOV flag. For example only, the OOV amount may indicate how often the drive controller 132 is operating OOV. For purposes of illustration only, the inverter power module 208 may define an operating region shaped like a hexagon. The voltage demands may be thought of as circles within the hexagon. If the circles are centered within the hexagon, as the circles expand, they will touch the sides of the hexagon. When the circles expand beyond the hexagon, the circles become more and more clipped at each face of the hexagon. Clipping may correspond to the OOV state. As a result, the proportion of time that the voltage demands are clipping (producing the OOV state) indicates how far OOV the drive controller 132 is.

The OOV amount may represent a portion of the time that the drive controller 132 is spending in the OOV state. The OOV amount may be determined by applying a filter, such as a digital low-pass filter, to the OOV flag. For example only, the OOV amount may be determined by applying a moving average to the OOV flag. When the OOV flag assumes values of 0 or 1, the OOV amount will then range between 0 and 1, inclusive. When multiplied by 100, the OOV amount is the percentage of time the drive controller 132 is spending in the OOV state.

The motor control module 260 may use multiple approaches to minimize OOV operation, or to maintain OOV operation below a predetermined threshold. In various implementations, the Idr injection module 512 may use the OOV amount in determining how to adjust the Idr demand. The speed loop control module 510 may also use the OOV amount to determine when to suspend increases in the demanded torque. The current control module 516 may suspend increases to one or both of the Vqr and Vdr commands based on the OOV flag. Additionally or alternatively, the current control module 516 may suspend integrator action when the OOV signal is generated.

Referring now to FIG. 6, a functional block diagram of an example implementation of the estimator module 504 is shown. The estimator module 504 can use the voltage commands and the measured currents provided in any FoR, such as the theta-v FoR. A three phase permanent magnet motor may be described by a set of equations in the so-called terminal variable or abc frame of reference. Operation of the motor 400 may be controlled such that the sum of currents across the three phases is zero. The equations recast in the alpha-beta frame of reference may be written as:

  λ_(αβ 0) = λ_(f) ⋅ C ⋅ P(θ_(r)) + C ⋅ L_(Cabc) ⋅ C⁻¹ ⋅ I_(αβ 0) + C ⋅ L_(Vabc)(θ_(r)) ⋅ C⁻¹ ⋅ I_(αβ 0) $V_{{\alpha\beta}\; 0} = {{R_{{\alpha\beta}\; 0} \cdot I_{{\alpha\beta}\; 0}} + {\lambda_{f} \cdot \omega_{r} \cdot C \cdot {Q\left( \theta_{r} \right)}} + {{L_{C\;{\alpha\beta}\; 0} \cdot \frac{d}{dt}}I_{{\alpha\beta}\; 0}} + {{\frac{d}{dt}\left\lbrack {L_{V\;{\alpha\beta}\; 0}\left( \theta_{r} \right)} \right\rbrack} \cdot I_{{\alpha\beta}\; 0}} + {{{L_{V\;{\alpha\beta}\; 0}\left( \theta_{r} \right)} \cdot \frac{d}{dt}}I_{{\alpha\beta}\; 0}}}$

These equations may be re-written in a rotating FoR. In particular, the equations can be re-written in the FoR defined by demanded speed (the qdv FoR):

  λ_(Qdv) = λ_(f) ⋅ U_(y) + L_(Qdv) ⋅ I_(Qdv) $V_{Qdv} = {{R_{Qdv} \cdot I_{Qdv}} + {\omega_{v} \cdot \lambda_{f} \cdot U_{x}} + {{L_{Qdvr} \cdot \frac{d}{dt}}I_{Qdv}} + {\omega_{v} \cdot G \cdot L_{Qdv} \cdot {I_{Qdv}.}}}$

From these equations, state and measurement equations used by a flux estimation module 604 can be derived. For example only, the flux estimation module 604 may include a Luenberger observer, a functional block diagram of which is illustrated by 700 in FIG. 7. While use of a Luenberger observer is shown and described, the flux estimation module 604 may generate an estimated magnet flux and/or an estimated total flux using another suitable flux estimator, such as using a linear Kalman filter, an extended Kalman filter, an ensemble Kalman filter, an unscented Kalman filter, another suitable type of Kalman filter, or another suitable type of filter or observer.

The flux estimation module 604 may generate the estimated magnet flux and/or the estimated total flux based on the measured currents, the output speed ω_(r), the commanded speed ω_(v), and the voltage commands. The flux estimation module 604 may generate the estimated magnet flux and/or the estimated total flux further based on Q-axis resistance (R_(q)) of the motor 400, d-axis resistance (R_(d)) of the motor 400, Q-axis inductance (L_(q)) of the motor 400, and d-axis inductance (L_(d)) of the motor 400.

An angle estimation module 608 generates the estimated angle θ_(est) based on at least one of the estimated magnet flux and the estimated total flux. A speed estimation module 612 generates the estimated speed ω_(est) based on the estimated angle θ_(est). For example, the speed estimation module 612 may differentiate and filter the estimated angle θ_(est) over a period of time to determine the estimated speed ω_(est). In various implementations, the angle estimation module 608 may generate the estimated angle θ_(est) using the equation: θ_(est) =a tan 2(λ_(fQv),λ_(fdv)), where a tan 2 is the two-argument (four-quadrant) arctangent function, and λ_(fQv) and λ_(fdv) are the Q and d axis magnet flux linkages.

For the case of a Luenberger observer, as illustrated by FIG. 7, the following state and measurement equations can be derived. As used above, C refers to the 3 to 2 static FoR transformation, Clark's Transformation. Below, C is the measurement matrix and maps the estimated states to measurements.

$\frac{d\hat{x}}{dt} = {{A \cdot \hat{x}} + {B \cdot u} + {K \cdot \left( {y - {C \cdot \hat{x}}} \right)}}$ e = (y − C ⋅ x̂)

In the system defined by the above equations, the observer matrices are defined by the equations:

${{\frac{d}{dt}\begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}} = {{\begin{pmatrix} \frac{- R}{L + M} & {- \omega_{v}} & \frac{R}{L + M} & 0 \\ \omega_{v} & \frac{- R}{L + M} & 0 & \frac{R}{L + M} \\ 0 & 0 & 0 & {- \left( {\omega_{v} - \omega_{r}} \right)} \\ 0 & 0 & \left( {\omega_{v} - \omega_{r}} \right) & 0 \end{pmatrix} \cdot \begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}} + {\begin{pmatrix} 1 & 0 \\ 0 & 1 \\ 0 & 0 \\ 0 & 0 \end{pmatrix} \cdot \begin{pmatrix} V_{Qv} \\ V_{dv} \end{pmatrix}}}};$ $\mspace{20mu}{{{{and}\mspace{20mu}\begin{pmatrix} I_{Qv} \\ I_{dv} \end{pmatrix}} = {\begin{pmatrix} \frac{1}{L + M} & 0 & \frac{- 1}{L + M} & 0 \\ 0 & \frac{1}{L + M} & 0 & \frac{- 1}{L + M} \end{pmatrix} \cdot \begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}}},}$ where the A, B, and C matrices are expressed as:

${A = \begin{pmatrix} \frac{- R}{L + M} & {- \omega_{v}} & \frac{R}{L + M} & 0 \\ \omega_{v} & \frac{- R}{L + M} & 0 & \frac{R}{L + M} \\ 0 & 0 & 0 & {- \left( {\omega_{v} - \omega_{r}} \right)} \\ 0 & 0 & \left( {\omega_{v} - \omega_{r}} \right) & 0 \end{pmatrix}},{B = \begin{pmatrix} 1 & 0 \\ 0 & 1 \\ 0 & 0 \\ 0 & 0 \end{pmatrix}},{and}$ $C = {\begin{pmatrix} \frac{1}{L + M} & 0 & \frac{- 1}{L + M} & 0 \\ 0 & \frac{1}{L + M} & 0 & \frac{- 1}{L + M} \end{pmatrix}.}$

That is:

${A = \begin{pmatrix} {- \frac{R_{Q}}{L_{Q}}} & {- \omega_{v}} & \frac{R_{Q}}{L_{Q}} & 0 \\ \omega_{v} & {- \frac{R}{L_{d}}} & 0 & \frac{R_{d}}{L_{d}} \\ 0 & 0 & 0 & {\omega_{r} - \omega_{v}} \\ 0 & 0 & {- \left( {\omega_{r} - \omega_{v}} \right)} & 0 \end{pmatrix}},{B = \begin{pmatrix} 1 & 0 \\ 0 & 1 \\ 0 & 0 \\ 0 & 0 \end{pmatrix}},{C = \begin{pmatrix} \frac{1}{L_{q}} & 0 & \frac{- 1}{L_{q}} & 0 \\ 0 & \frac{1}{L_{d}} & 0 & \frac{- 1}{L_{d}} \end{pmatrix}},{x = \begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}},{u = \begin{pmatrix} V_{Qv} \\ V_{dv} \end{pmatrix}}$ where R_(q) is the Q-axis resistance of the motor 400, R_(d) is the d-axis resistance of the motor 400, L_(q) is the Q-axis inductance of the motor 400, and L_(d) is the d-axis inductance of the motor 400. λ_(Qv) and λ_(dv) are the total flux linkages. λ_(fQv) and λ_(fdv) are the magnet flux linkages.

From the estimate of the state derivative, the actual system state (at time k) can be obtained by integration from an initial condition (at time k−1):

$\begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}_{k} = {\begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}_{k - 1} + {{T_{s} \cdot \frac{d}{dt}}\begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}_{k}}}$

The estimated state is then referenced back to a measurable system state via the measurement equation: e=(y−C·{circumflex over (x)}), which can be re-written as:

$e = {\begin{pmatrix} I_{Qv} \\ I_{dv} \end{pmatrix} - {\begin{pmatrix} \frac{1}{L + M} & 0 & \frac{- 1}{L + M} & 0 \\ 0 & \frac{1}{L + M} & 0 & \frac{- 1}{L + M} \end{pmatrix} \cdot {\begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}.}}}$ Re-writing the C matrix (the measurement matrix) in terms of Q-axis inductance (L_(q)) and d-axis inductance (L_(d)) yields:

$C = {\begin{pmatrix} \frac{1}{L_{q}} & 0 & \frac{- 1}{L_{q}} & 0 \\ 0 & \frac{1}{L_{d}} & 0 & \frac{- 1}{L_{d}} \end{pmatrix}.}$

The flux estimation module 604 may generate the estimated magnet flux as a function of one or more of the magnet flux linkages (λ_(fQv) and λ_(fdv)). For example, the flux estimation module 604 may generate the estimated magnet flux using the equation: λ² _(f)=λ² _(fQv)+λ² _(fdv), where λ_(f) is the estimated magnet flux. The flux estimation module 604 may generate an estimated total flux as a function of one or more of the total flux linkages (λ_(Qv) and λ_(dv)). For example, the flux estimation module 604 may generate the estimated total flux using the equation: λ²=λ_(Qv) ²+λ_(dv) ², where λ is the estimated total flux.

The Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d) are variable values. A resistance determination module 616 determines the Q-axis resistance R_(q) and the d-axis resistance R_(d). An inductance determination module 620 determines the Q-axis inductance L_(q) and the d-axis inductance L_(d).

The resistance determination module 616 and the inductance determination module 620 determine the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d) as functions of a bulk current I_(B). For example only, the resistance determination module 616 may determine the Q-axis resistance R_(q) and the d-axis resistance R_(d) using the equations:

${R_{Q} = {\sum\limits_{k = 1}^{K_{RQ}}{C_{k}\bullet\; I_{NB}^{k - 1}}}};{and}$ ${R_{d} = {\sum\limits_{k = 1}^{K_{Rd}}{d_{k}\bullet\; I_{NB}^{k - 1}}}},$ where c and d are experimentally determined, predetermined coefficients that relate the normalized bulk current I_(NB) to the Q-axis resistance R_(q) and the d-axis resistance R_(d). In various implementations, the bulk current I_(B) may be used in place of the normalized bulk current I_(NB). The inductance determination module 620 may determine the Q-axis inductance L_(q) and the d-axis inductance L_(d), for example, using the equations:

${L_{Q} = {\sum\limits_{k = 1}^{K_{LQ}}{a_{k}\bullet\; I_{NB}^{k - 1}}}};{and}$ ${L_{d} = {\sum\limits_{k = 1}^{K_{Ld}}{b_{k}\bullet\; I_{NB}^{k - 1}}}},$ where a and b are experimentally determined, predetermined coefficients that relate the normalized bulk current I_(NB) to the Q-axis inductance L_(q) and the d-axis inductance L_(d). In various implementations, the bulk current I_(B) may be used in place of the normalized bulk current I_(NB). Coefficients a, b, c, and d are real numbers. While polynomial expressions for determining the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d) have been described, other suitable functions may be used to determine the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d) based on the bulk current I_(B). For example, an orthonormal polynomial function (e.g., a Chebyshev function), a trigonometric function, a neural network function, a fuzzy logic function, or a look-up table may be used.

A bulk current determination module 624 determines the bulk current I_(B) as a function of the measured currents (e.g., IQr and Idr). For example, the bulk current determination module 624 may determine the bulk current I_(B) using the following equation or another suitable mathematical relationship. I _(B)=√{square root over (I′ _(Qdv) ·I _(Qdv))}, where I_(Qdv) is a 1×2 Vector with Q-axis current (I_(Qv)) and d-axis current (I_(dv)) entries, and I_(Qdv)′ is the vector transpose of I_(Qdv). This equation can be re-written as: I _(B)=√{square root over (I _(Qv) ² +I _(dv) ²)}. The function for determining the bulk current I_(B) may be selected based on the functions that relate the bulk current I_(B) to the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d). In other words, the bulk current I_(B) can be determined using other functions.

In various implementations, a normalized version of the bulk current I_(B) may be used to determine the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d), as discussed above. The bulk current determination module 624 may generate the normalized version of the bulk current I_(B), for example, by dividing the bulk current I_(B) by a maximum allowable bulk current.

In various implementations, such as in the case of the Luenberger observer, one or more gains may be defined for specified pole locations. These gains may change with changes in one or more motor parameters (e.g., resistance or inductance). For example, one or more gain values (e.g., K in the Luenberger observer case) may be calculated using an average value of a motor parameter defined over the expected range of bulk currents, from the minimum to the maximum defined by [I₁, I₂]:

$\frac{1}{I_{2} - I_{1}} \cdot {\int_{\zeta = I_{1}}^{I_{2}}{\sum\limits_{k = 1}^{K}{{\alpha_{k} \cdot \zeta_{NB}^{k - 1}}d\;{\zeta.}}}}$ It may be assumed that the lower bound of the expected range is zero.

A gain setting module 628 sets one or more gain values (e.g., K in the Luenberger observer case and/or coefficients a-d used to determine the Q and d axis resistance and inductance values) used by the flux estimation module 604 to generate the estimated magnet flux and/or the estimated total flux. In an example, polynomials for each motor parameter may be determined and optimized to minimize the error between estimated and measured angles.

In another example, the gain setting module 628 may set the one or more gain values based on one or more of the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d). For example, an average of the Q-axis resistance R_(q) and the d-axis resistance R_(d) may be determined, an average of the Q-axis inductance L_(q) and the d-axis inductance L_(d) may be determined, and the gain setting module 628 may determine one or more gain values as a function of the averages. In various implementations, the averages may be weighted, for example, with respect to a range of the bulk current I_(B), and the one or more gain values may be determined as a function of the weighted averages.

In another example, the one or more gain values may be determined as a function of the bulk current I_(B). The one or more gain values may be updated at a rate that is equal to or slower than the rate at which the flux estimation module 604 generates the estimated magnet flux and/or the estimated total flux.

In another example, the one or more gain values may be determined as a function of the bulk current I_(B) and a speed of the motor 400, such as the estimated speed ω_(est), the output speed ω_(r), or the commanded speed the output speed ω_(v). The one or more gain values may be updated at a rate that is equal to or slower than the rate at which the flux estimation module 604 generates the estimated magnet flux and/or the estimated total flux. In various implementations, the resistance and inductance averages can be used and the gains can change dynamically based on the estimated speed ω_(est), the output speed ω_(r), or the commanded speed the output speed ω_(v).

FIG. 8 includes an example graph 804 of how d-axis resistance and Q-axis resistance may change with bulk current I_(B). FIG. 8 also includes an example graph 808 illustrative of how d-axis inductance and Q-axis inductance may change with bulk current I_(B).

Referring now to FIG. 9, a flowchart depicting an example method of generating the estimated position and the estimated speed of the motor 400 is presented. Control may begin with 904 where control determines the bulk current. Control may determine the bulk current I_(B), for example, using the equation: I _(B)=√{square root over (I′ _(Qdv) ·I _(Qdv))}, where I_(Qdv) is a 1×2 Vector with Q-axis current (I_(Qv)) and d-axis current (I_(dv)) entries, and I_(Qdv)′ is the vector transpose (2×1 vector) of I_(Qdv). This equation can be re-written as: I _(B)=√{square root over (I _(Qv) ² +I _(dv) ²)}. The function for determining the bulk current I_(B) may be selected based on the functions that relate the bulk current I_(B) to the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d). In other words, the bulk current I_(B) can be determined using other functions.

At 908, control may determine the d-axis resistance, the Q-axis resistance, the d-axis inductance, and the Q-axis inductance. Control determines the d-axis resistance, the Q-axis resistance, the d-axis inductance, and the Q-axis inductance as functions of the bulk current I_(B). In various implementations, the normalized version of the bulk current I_(B) may be used to determine the d-axis resistance, the Q-axis resistance, the d-axis inductance, and the Q-axis inductance. For example only, the d-axis resistance, the Q-axis resistance, the d-axis inductance, and the Q-axis inductance using the equations:

${L_{Q} = {\sum\limits_{k = 1}^{K_{LQ}}{a_{k}\bullet\; I_{NB}^{k - 1}}}};$ ${L_{d} = {\sum\limits_{k = 1}^{K_{Ld}}{b_{k}\bullet\; I_{NB}^{k - 1}}}};$ ${R_{Q} = {\sum\limits_{k = 1}^{K_{RQ}}{c_{k}\bullet\; I_{NB}^{k - 1}}}};{and}$ ${R_{d} = {\sum\limits_{k = 1}^{K_{Rd}}{d_{k}\bullet\; I_{NB}^{k - 1}}}},$ where a and b are experimentally determined, predetermined coefficients that relate the bulk current I_(B) to the Q-axis inductance L_(q) and the d-axis inductance L_(d), c and d are experimentally determined, predetermined coefficients that relate the bulk current I_(B) to the Q-axis resistance R_(q) and the d-axis resistance R_(d), and coefficients a, b, c, and d are real numbers. While polynomial expressions for determining the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d) have been described, another suitable function may be used to determine the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d) based on the bulk current I_(B), such as an orthonormal polynomial function (e.g., a Chebyshev function), a trigonometric function, a neural network function, a fuzzy logic function, or a look-up table.

At 912, control determines and sets the one or more gain values used to generate the estimated magnetic flux and/or the estimated total flux. For example, one or more gain values may be calculated using an average value of a motor parameter defined over the expected range of bulk currents; or, polynomials for each motor parameter may be determined and optimized to minimize the error between estimated and measured angles or as a function of the averages. Typically the polynomials have an order in the range of zero (constant) to cubic, and the q and d-axis values may or may not be coincident.

For another example, control may determine the one or more gain values based on the average of the Q-axis resistance R_(q) and the d-axis resistance R_(d) and the average of the Q-axis inductance L_(q) and the d-axis inductance L_(d), based on the weighted averages, based on the bulk current, or based on the bulk current and a speed of the motor 400, such as the estimated speed ω_(est), the output speed ω_(r), or the commanded speed the output speed ω_(v). In various implementations, the resistance and inductance averages can be used and the gains can change dynamically based on the estimated speed ω_(est), the output speed ω_(r), or the commanded speed the output speed ω_(v). Control may alternatively determine the one or more gain values as a function of load or bulk current.

At 916, control generates the estimated magnet flux and/or the estimated total flux. Control generates the estimated magnet flux and/or the estimated total flux as functions of the Q-axis resistance R_(q), the d-axis resistance R_(d), the Q-axis inductance L_(q), and the d-axis inductance L_(d). Control generates the estimated angle θ_(est) of the motor 400 as a function of at least one of the estimated magnet flux and the estimated total flux at 920. Control may generate the estimated speed ω_(est) of the motor 400 based on the estimated angle θ_(est) of the motor 400 at 924. In various implementations, control may generate the estimated speed ω_(est) of the motor 400 in another suitable manner, such as by solving an over-determined equation for the estimated speed ω_(est).

Referring now to FIG. 10, an example method for assessing estimator convergence is shown. Control starts in 1004, where the motor drive is started in open loop mode. Control continues at 1008, where the estimator is started. Control continues at 1012, where control begins calculating an average of total flux linkage derivatives. The control continues at 1016, where control begins calculating variance of the total flux linkage derivatives. The derivatives may be determined based on the averages from 1012. This calculation continues while the motor is operating in open loop, and may stop or may continue when the motor is operating in closed loop mode. For example, the variance may be calculated as follows: Variance=[dλ _(Qv) /dt−Avg(dλ _(Qv) /dt)]² +[dλ _(dv) /dt−Avg(dλ _(dv) /dt)]². In various implementations, variance of total or magnet flux linkages may be used. In various implementations, each of the constituents of the variance equation above (within the brackets) may be filtered (e.g., averaged) before being squared.

Control continues at 1020, where a Counter is initialized to 0. The Counter tracks convergence of the estimator and increases as the estimator converges with the motor and decreases as the estimator diverges from the motor. Control also clears a Decrement_Flag, which is used to control decrementing the Counter when the estimator is no longer diverging from the motor but is not converging.

Control also initializes a Timer to a startup value. This startup value may correspond to a maximum length of time within which startup of the motor is expected to occur. In other words, if the motor has not completely started by the time the Timer expires, it is likely that a problem is present. The startup value may also be based on the amount of time within which the estimator should converge with motor operation. When it takes longer for the estimator to converge with the motor than it takes the motor to start up, the convergence time may govern the startup value.

Control continues at 1024, where control evaluates the variance from 1016. If the variance is less than or equal to one, control transfers to 1028; otherwise, control transfers to 1032. The value of one is shown for example only and may be determined based on motor and estimator characterizations and or may vary dynamically based on motor operating parameters. At 1028, because the variance is low, the Decrement_Flag is cleared. This indicates that, even if the variance increases slightly, decrementing should not be performed because the variance was previously small. Control continues at 1036, where a Counter is incremented to indicate the low variance. Control then continues at 1040.

At 1032, control determines whether the variance is greater than three, and if so, transfers to 1044; otherwise, control transfers to 1048. Again, the value of three is given as an example only, and may be predetermined or may vary dynamically. At 1044, because the variance is considered large, the Decrement_Flag is set. Control continues at 1052, where the Counter is decremented. In various implementations, the Counter may have a lower limit, such as zero—therefore, the Counter will not be decremented below zero. Control then continues at 1040.

At 1048, the variance is considered neither high nor low, and the Decrement_Flag is evaluated. If the Decrement_Flag is set, control transfers to 1052 to decrement the Counter; otherwise, control continues at 1040. At 1040, control determines whether the Counter is equal to a predetermined value, such as one-hundred fifty (150), indicating that the estimator has converged. If so, control transfers to 1056; otherwise, control transfers to 1060.

At 1060, if the Timer has expired, this indicates that the estimator has not converged within the expected timeframe and an error has occurred. Therefore, if the Timer has expired, control transfers to 1064; otherwise, control returns to 1024. At 1064, control signals a rotor fault condition, which may indicate a locked rotor, meaning that the rotor is physically stuck, or a lost rotor, meaning that the position of the rotor is not being accurately estimated for some reason. Control continues at 1068, where remedial action is performed. In the implementation of FIG. 10, the motor drive is shut down. Control then stops. Control may try to restart the motor, possibly after a predetermined delay, at which point control will restart at 1004.

At 1056, control switches the drive to closed loop mode. At this point, a gradual transition from open loop control angle and open loop speed to closed loop control angle and closed loop speed may begin. Control continues at 1072, where the Timer is initialized to a transition value. The transition value may be set based on a maximum period of time in which a transition may occur. For example, the transition value may be set based on the time it would take to transition if the starting difference between the open loop control angle and the closed loop control angle was at the maximum possible value.

During the transition from open loop to closed loop, convergence estimates may be unreliable, and therefore incrementing or decrementing of the Counter may be paused. In FIG. 10, this is implemented by waiting for the transition value of time to lapse. Therefore control continues at 1076, where control remains until the Timer expires. Control then continues at 1080, where control begins monitoring another motor parameter, such as the magnitude of magnet flux linkages. At this time, the average variance calculation of 1012 and 1016 may be halted. For example only, the magnitude of magnet flux linkages may be calculated as follows: λf=√{square root over (λ² _(fQv)+λ² _(fdv))},

where λ_(fQv) and λ_(fdv) are the magnet flux linkages. In various implementations, the square of λ_(f) can be used (i.e., λ_(f) ²). This equation can be re-written using vector notation as: λf=√{square root over (λ′_(fQdv)·λ_(fQdv))} where λ_(fQdv) is a 2×1 Vector with Q-axis magnet flux linkage (λ_(fQv)) and d-axis magnet flux linkage (λ_(fdv)) entries, and λ_(fQdv)′ is the vector transpose (1×2 vector) of λ_(fQdv).

At 1084, control evaluates the magnitude from 1080. If the magnitude is greater than a threshold, such as 0.004, control transfers to 1088; otherwise, control transfers to 1092. At 1088, control increments the Counter and continues at 1096. An upper limit may be imposed on the Counter, such as 150, meaning that the Counter will not be incremented above that upper limit. At 1092, the Counter is decremented and control continues at 1096. At 1096, control compares the Counter to a lower threshold, such as 120. If the Counter has decreased to 120 or below, this is considered to be a loss of convergence, and control transfers to 1064; otherwise, control returns to 1084.

Variations on the counter scheme are encompassed by the present disclosure and may be logically equivalent. For example, incrementing can be performed using a negative or positive integer. In other words, in an implementation where the incrementing is by positive one, the counter increases from zero to one-hundred fifty as the estimator converges. Alternatively, in an implementation where the incrementing is by negative 1, the counter decreases from one-hundred fifth to zero as the estimator converges.

Referring now to FIG. 11, an example implementation of the rotor check module 503 is shown. An averaging module 1104 receives estimator parameters from the estimator module 504. The averaging module 1104, may calculate averages of the derivative of total flux linkages. A statistical module 1108 determines a statistical parameter of estimator parameters. For example, the statistical module 1108 calculates a variance of the derivative of total flux linkages.

A multiplexer 1112 is controlled by an output of a transition module 1116. The transition module 1116 may output a transition signal indicating closed loop or open loop mode. When the transition signal changes from open loop to closed loop, an angle and speed transition may begin, as described above.

When the transition signal indicates open loop mode, the multiplexer 1112 selects the statistical module 1108 as the output from the multiplexer 1112. When the transition signal changes to closed loop, the multiplexer 1112 selects an input from a magnitude module 1120. The magnitude module 1120 calculates a magnitude of estimator parameters. For example only, the magnitude module 1120 may calculate the magnitude of magnet flux linkages.

The output of the multiplexer 1112 is received by an evaluation module 1124. The evaluation module 1124 compares the output of the multiplexer 1112 to one or more thresholds received from a thresholds module 1128. The thresholds provided by the thresholds module 1128 may be determined based on the state of the transition signal.

The evaluation module 1124 may also receive the transition signal to determine how to adjust a Counter, which is maintained by a counter module 1130. For example only, in the closed loop mode, the evaluation module 1124 may compare the output of the multiplexer 1112 to a single threshold and increment or decrement the Counter based on that comparison. Meanwhile, in open loop mode, the evaluation module 1124 may compare the output of the multiplexer 1112 to a pair of thresholds, (i) decrement the Counter when the output is greater than the greater threshold, (ii) increment the Counter when the output is less than the lower threshold, and (iii) only if the Counter was already decrementing, decrement the Counter when the output is between the thresholds.

The counter module 1130 stores the Counter value, which is provided to the transition module 1116 and to a fault module 1132. The transition module 1116 may change the transition signal from open loop to closed loop once the output of the counter module 1130 reaches a predetermined value.

A timer module 1136 keeps track of time from when the motor starts. For example only, the timer may be initialized to a maximum expected value of the larger of motor start time and estimator convergence time. Once that timer expires, if the transition signal has not changed to closed loop mode, indicating estimator convergence, the fault module 1132 may declare a rotor fault. In various implementations, this may lead to shut down of the motor drive. The fault module 1132 may also monitor the output of the counter module 1130 while in closed loop mode. If the output of the counter module 1130 falls below a predetermined threshold, the fault module 1132 signals the rotor fault.

The counter module 1130 may freeze—i.e., not increment or decrement—once the transition module 1116 signals a change from open loop to closed loop. The timer module 1136 may further keep track of the time elapsed since the transition module 1116 signaled the change from open loop to closed loop. After a predetermined time, the timer module 1136 expires, and the expiration signal is used by the counter module 1130 to unfreeze incrementing and decrementing.

Although certain examples of estimator parameters are described above, additional or alternative estimator parameters may be used to evaluate convergence of the estimator. These include, but are not limited to, absolute value of the estimated magnet flux, variance of the absolute of the estimated magnet flux, and variance in the dot inner product of the signal:

$\frac{d}{dt}\begin{pmatrix} \lambda_{Qv} \\ \lambda_{dv} \\ \lambda_{fQv} \\ \lambda_{fdv} \end{pmatrix}$ where λ_(Qv) and λ_(dv) are the total flux linkages and λ_(fQv) and λ_(fdv) are the magnet flux linkages.

The averaging module 1104 may use a rolling average, such as the following:

${y(k)} = {{\frac{1}{f} \cdot {x(k)}} + {\frac{1 - f}{f} \cdot {y\left( {k - 1} \right)}}}$ In the above equation, x(k) is the input value, y(k) is the output value, and f is a weighting factor, which may be referred to as a forgetting factor. The value f may be set within the range of 0 to 1 exclusive. As f increases toward 1, the contribution of previous values is lessened.

While the description of the Counter above refers to incrementing and decrementing by a value of 1, the Counter may be incremented or decremented by other integer or noninteger values. For example only, the Counter may be decremented by larger integer values when the variance is larger. For example, the size of the decrement may be proportional to the difference between the variance and the threshold. In various implementations, instead of being directly proportional, a logarithmic relationship may be used so that very large temporary variances are not given disproportionate weight. In other implementations, the increment or decrement performed by the Counter may be based on a function that uses an input parameter and a rate of change of an input parameter; the input parameter in one example is variance.

Further estimator parameters used by the rotor check module 503 may include flux linkage as estimated by the observer, magnet flux as estimated by the observer, derivative of flux linkage from the observer, derivative of magnet flux from the observer, and an error term calculated from a measurement equation. Any one or more of the above parameters may be transformed into an alternative frame of reference. For example, the observer may use a drive frame of reference, making it possible to transform the above parameters to a stationary frame of reference, an alternative rotating frame of reference, or an estimated electrical frame of reference. Further, two or more of the above parameters may be evaluated in determining convergence.

Although variance is the statistical parameter used as an example above, alternative statistical measures, such as standard deviation, may be used. In addition, other statistical tests, such as the chi-squared test, may be used. Further, other methods, which may be more computationally demanding, can be used. For example, see the cumulative sum algorithm, described in M. Basseville, I. Nikiforov, Detection of Abrupt Changes: Theory and Applications, ISBN-13: 978-0131267800, the disclosure of which is hereby incorporated by reference in its entirety.

Although the estimator above is described as being a Luenberger observer, alternative estimations processes may be used, such as a Kalman filter. For example, the Kalman filter may be a linear Kalman filter, an extended Kalman filter, an ensemble Kalman filter, an unscented Kalman filter, etc. See Dan Simon, Optimal State Estimation: Kalman, H-Infinity and Nonlinear Approaches, ISBN-13: 978-0471708582, the disclosure of which is hereby incorporated by reference in its entirety.

The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.

In this application, including the definitions below, the term module may be replaced with the term circuit. The term module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; memory (shared, dedicated, or group) that stores code executed by a processor; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared processor encompasses a single processor that executes some or all code from multiple modules. The term group processor encompasses a processor that, in combination with additional processors, executes some or all code from one or more modules. The term shared memory encompasses a single memory that stores some or all code from multiple modules. The term group memory encompasses a memory that, in combination with additional memories, stores some or all code from one or more modules. The term memory may be a subset of the term computer-readable medium. The term computer-readable medium does not encompass transitory electrical and electromagnetic signals propagating through a medium, and may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory tangible computer readable medium include nonvolatile memory, volatile memory, magnetic storage, and optical storage.

The apparatuses and methods described in this application may be partially or fully implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on at least one non-transitory tangible computer readable medium. The computer programs may also include and/or rely on stored data. 

What is claimed is:
 1. A method of operating an electric motor, the method comprising: starting the electric motor in an open loop control mode; using an estimator module, estimating derivatives with respect to time of total flux linkages of the electric motor based on at least one measured parameter of the electric motor; while the electric motor is in the open loop control mode, evaluating the derivatives of the total flux linkages estimated by the estimator module; in response to the evaluation of the derivatives of the total flux linkages, determining whether the estimator module has converged; and in response to a determination that the estimator module has not converged within a predetermined period of time after starting the electric motor, signaling a first fault condition and at least one of: (i) shutting down the electric motor; and (ii) restarting the electric motor.
 2. The method of claim 1 wherein the electric motor is a compressor motor.
 3. The method of claim 1 further comprising: switching to a closed loop control mode; while the electric motor is in the closed loop control mode, evaluating a parameter of the estimator module; and in response to the evaluation of the parameter, selectively signaling a second fault condition.
 4. The method of claim 3 further comprising signaling both the first fault condition and the second fault condition using a common 1-bit signal.
 5. The method of claim 1 wherein the evaluating the derivatives of the total flux linkages includes calculating a variance of the total flux linkage derivatives.
 6. The method of claim 3 wherein the parameter includes magnet flux linkages.
 7. The method of claim 6 wherein the evaluating the parameter includes calculating a magnitude of the magnet flux linkages.
 8. The method of claim 3 wherein the evaluating the parameter includes: comparing a measure of the parameter with a threshold; incrementing a counter in response to the measure being greater than the threshold; and decrementing the counter in response to the measure being less than the threshold.
 9. The method of claim 8 further comprising applying an upper limit to the counter, wherein the counter is incremented only up to the upper limit.
 10. The method of claim 8 further comprising signaling the second fault condition in response to the counter being decremented to a lower limit.
 11. The method of claim 8 further comprising, for a second predetermined period of time beginning at the switch to closed loop mode, suspending incrementing the counter and decrementing the counter.
 12. The method of claim 1 wherein the evaluating the derivatives of the total flux linkages includes: comparing a measure of the derivatives of the total flux linkages to (i) a lower threshold and (ii) an upper threshold that is greater than the lower threshold; incrementing a counter in response to the measure being less than the lower threshold; and decrementing the counter in response to the measure being greater than the upper threshold.
 13. The method of claim 12 wherein the evaluating the derivatives of the total flux linkages further includes, in response to the measure being between the lower threshold and the upper threshold, decrementing the counter in response to the counter being decremented immediately previously.
 14. The method of claim 12 further comprising determining that the estimator module has converged in response to the counter being incremented to an upper limit.
 15. The method of claim 12 wherein the evaluating the derivatives of the total flux linkages further includes applying a lower limit to the counter, wherein the counter is decremented only down to the lower limit.
 16. The method of claim 3 wherein switching to the closed loop control mode is performed in response to a determination that the estimator module has converged.
 17. The method of claim 3 wherein switching to the closed loop control mode is performed when the predetermined period of time has passed after starting the electric motor.
 18. A control system for an electric motor, the control system comprising: an estimator module that estimates derivatives of total flux linkages with respect to time of the electric motor based on at least one measured parameter of the electric motor; and a rotor check module that: commands operation of the electric motor in an open loop control mode at startup of the electric motor; while the electric motor is in the open loop control mode, evaluates the derivatives of total flux linkages estimated by the estimator module; in response to the evaluation of the derivatives of total flux linkages, determines whether the estimator module has converged; and in response to a determination that the estimator module has not converged within a predetermined period of time after starting the electric motor, signals a first fault condition and at least one of: (i) shuts down the electric motor; and (ii) restarts the electric motor.
 19. The control system of claim 18 wherein the rotor check module further: commands a transition to operating the electric motor in a closed loop control mode; while the electric motor is in the closed loop control mode, evaluates a parameter of the estimator module; and in response to the evaluation of the parameter, selectively signals a second fault condition.
 20. The control system of claim 18 wherein: the evaluation of the derivatives of the total flux linkages includes the rotor check module calculating a variance of the total flux linkage derivatives while the electric motor is in the open loop control mode; and the determination of whether the estimator module has converged includes the rotor check module determining whether the estimator module has converged based on the variance of the total flux linkage derivatives. 